Not by the name "Trinity" but the Holy Spirit is mentioned in the first verse of The Bible and Jesus visits Abraham and Samsons parents, as well as Shadrak, Meshak and Abendigo (don't know correct spelling on their names). God is also mentioned of course numorous times so I think that the Holy Trinity is mentioned often, though not by name.
Another Answer:
The term 'holy trinity' is not Scriptural. It is a vain attempt by men in the 4th Century, AD, to describe the Godhead - confusing God's Holy Spirit as a person.
The Holy Spirit is not a separate person or being, but is rather the power and the means by which God transmits His will, influence and presence.
Rather than describing the Holy Spirit as a distinct person or entity, the Bible most often refers to it as, and connects it with, God's divine power (Zechariah 4:6; Micah 3:8). Jewish scholars, examining the references to it in the Old Testament Scriptures, have never defined the Holy Spirit as anything but the power of God.
In the New Testament, Paul referred to it as the spirit of power, love and a sound mind (2 Timothy 1:7). Informing Mary that Jesus would be supernaturally conceived in her womb, an angel told her, "The Holy Spirit will come upon you . . . ," and he defined this as "the power of the Highest," which "will overshadow you" (Luke 1:35). Jesus always said He is His Father's Son and no one elses.
The gifts are mentioned in the new testament and not in the old testament. Mostly in the books of Paul.
The colt, donkey ass were mentioned in the old testament.
Most likely God is mentioned in the Old Testament in what he said and did for His people.
The name is mentioned 26 times in the Old Testament.
In the King James translation, "Holy Ghost" is mentioned eighty-nine times; all in the New Testament.AdditionallyThe exact phase "Holy Ghost" is not mentioned in the Old Testament, however, many Christian biblical scholars say that references to the "Spirit of the Lord" (e.g. Judges 3:10, Ezekiel 11:5, etc.) or similar phrases in Old Testament is the same reference to the third person of God (namely the Holy Ghost) in New Testament. This view is generally not accepted among non-Christians.
The Passover
The hebrew word "Qodesh", (קֹדֶשׁ) often translated as "holy" or "set-apart" is mentioned 470 times in the TaNaKh (Old Testament).
The gifts are mentioned in the new testament and not in the old testament. Mostly in the books of Paul.
Holy Trinity Church - Old Swedes - was created in 1799.
The colt, donkey ass were mentioned in the old testament.
The concept of the Holy Trinity arose in the third century of Christianity and was formally adopted by the Council of Nicaea in the fourth century, after spirited argument. The Bible never mentions the Holy Trinity, and therefore never says that the Holy Spirit is the third person. A passage known as the "Johannine Comma" (1 John 5:7) does refer indirectly to the concept of the Trinity, but was never in the early Greek manuscripts, only appearing in the Latin translation of the fifth century, after the Trinity doctrine had been accepted by the Council of Nicaea.
Abraham is first mentioned in the Old Testament.
Most likely God is mentioned in the Old Testament in what he said and did for His people.
The name is mentioned 26 times in the Old Testament.
In the King James translation, "Holy Ghost" is mentioned eighty-nine times; all in the New Testament.AdditionallyThe exact phase "Holy Ghost" is not mentioned in the Old Testament, however, many Christian biblical scholars say that references to the "Spirit of the Lord" (e.g. Judges 3:10, Ezekiel 11:5, etc.) or similar phrases in Old Testament is the same reference to the third person of God (namely the Holy Ghost) in New Testament. This view is generally not accepted among non-Christians.
The word "Heaven" is mentioned 266 times in the Old Testament.
People were filled with the Holy Spirit.